The invention relates to a bit holder for a ploughing bit of a coal or extraction plough. In one embodiment, the bit holder includes an insert pocket open on the top face for reception of a bit shank formed on the ploughing bit, which is bounded by two lateral supporting walls, a front and a rear supporting wall, whereby the rear supporting wall exhibits an elevated section that projects above the adjacent side supporting walls, forms a bit support for the ploughing bit, is arranged primarily or essentially in the central region of the rear supporting wall, and slopes down to its outer regions.
In the bit holder known from DE-U 298 03 944, the elevated section supporting the back face of the ploughing bit projects only a short distance above the lateral supporting walls and therefore offers only slightly better support for the bit than a bit holder in which all four supporting walls are approximately the same height. The slightly better support of the bit provided by the higher rear supporting wall is generally associated with the disadvantage that coal dust can be deposited and compacted in the region of the rear supporting wall, as a result of which it is far more difficult to dismantle the bit. The reason for the increased accumulation of coal dust in the region of the higher rear supporting wall lies in the fact that the elevated section in the case of bit holders of known art is provided over practically its whole width and as a result a kind of gusset-type fillet groove is formed at the side near the inserted bit between the lateral supporting walls and the outer higher regions of the rear supporting wall, in which the fine coal can easily be deposited.
In order to avoid the disadvantages of an undesired deposit of fine coal in the transition region between the lateral supporting walls and the rear supporting wall it is proposed in the generic DE 299 01 985 to form the elevated section only in the central region of the rear supporting wall, whereby the rear supporting wall is then to slope down to its outer regions, as a result of which the front of the rear supporting wall, facing the ploughing bit and the insert pocket, exhibits in the outer regions deflectors that slope down and run outwards in the opposite direction to the work flow of the ploughing bit. As the elevated section forming the bit support only projects slightly at the side above the inserted ploughing bit, there is no significant dead space between the ploughing bit, the lateral supporting walls and the outer regions of the rear supporting wall. In addition, the deflectors aligned diagonally against the work flow direction of the ploughing bit are to ensure that fine coal that is blown against the work flow direction of the ploughing bit from its bit tip in the direction of the rear supporting wall, is guided diagonally outwards.
The generic bit holder reduces the tendency for fine coal to collect in the gusset, however, the installation of a new bit, e.g. in the event of replacement of all or individual ploughing bits as required by wear and tear, is made considerably more difficult as a result of the configuration with the outward-directed deflectors, extending almost as far as the insert pocket.
Thus, there is a need for a bit holder that allows good support for an inserted bit and easy and fast installation of the bit.